PURPOSE: To eliminate the difference in the contraction amount of a resin sheet by equally cooling the back and front surfaces of the resin sheet, by forcibly blasting a cooling medium against the back surface of the resin sheet while feeding the resin sheet of a semi-molten state on a reticulated belt conveyor.

CONSTITUTION: A reticulated belt conveyor 1 is driven to the direction shown by the arrow 1 by the rotation of a drive roller 2 and, at the same time, the water feeder 13 of a water cooling apparatus 9 is operated to supply water W to the supply pipes 11 connected to both ends of said water feeder while water W is injected toward the front and back surfaces of the belt conveyor 1 from nozzles 12 to cool said belt conveyor 1. The semi-molten resin sheet 1 placed to the upper surface of the belt conveyor 1 is cooled by the cooled belt conveyor 1 and, when fed above the water cooling apparatus 9, receives the blowing of injected water. Therefore, the resin sheet M is equally cooled from the front, side and back surfaces thereof to be prevented from feed inferiority such as deformation due to the difference in a contraction amount and the generation of molding inferiority at the time of stamping molding is prevented.